Balance of system [BOS]

With balance of system (BOS) we mean a system of control and conditioning of the power of a photovoltaic or wind power plant. It expresses in percentage the energy losses that are in the plant due to various factors, such as: the coupling between the various photovoltaic modules, the connections with the converter(s), the losses in the panels, in the conductors, etc..

Provides for maximum power point tracking device. Often includes the converter from direct current to alternating current, adapters of the output voltage of the system to the network voltage, filtering of harmonics, power factor correction and, for stand-alone systems, a battery charge controller.

As an indication, these are the main energy losses suffered by photovoltaic systems:

  • power losses = due to deviation from STC conditions: 5% if the climatic characteristics (temperature) of the place where the plant is located
  • reflection losses = 2÷3%.
  • mismatch losses = 3÷5%.
  • losses due to voltage drop on DC section = 1÷2%.
  • losses in the inverter = 5-10%.
  • losses due to dirt = 1÷2%.
  • Losses due to annual efficiency drop = 1÷2%.
  • losses in the voltage transformer (when present) = 3-6%.
  • losses due to voltage drop in the AC section = 1÷2%.
  • losses due to shading
  • loss due to the presence of snow
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